patches of different green shades

coengMay 29, 2012

Any idea what the patches in the photos below are the result of? No one in my neighborhood seems to have them, not even my next door neighbor as you can see in the first photo. In the morning when the grass is wet, it is most noticeable.

I just bought my house last Summer and tried a fungus killer in the Fall but that didn't seem to do anything.

This year I applied Johnathon Green's Mag-i-cal, JG's Step 1 pre-emergent, and most recently JG's Step 2 Weed and Feed, and still no change in appearance.

Those areas are most likely creeping bentgrass. Creeping bent has a bluish hue to it, especially when it is at lawn heights and covered with dew. Tenacity herbicide will selectively remove creeping bent from your lawn with little damage to your other turfgrass.

Will this product kill all of that grass in that area and leave a brown patch? Kind of like a selective Roundup targeted at bentgrass? Should I wait until the Fall so I can re-seed with a few days of killing it off?

Well first the bent will turn white, as Tenacity inhibits photosynthesis. Then the bent will wilt and die. If the areas are mostly bent then the area will be pretty thin after the bent wilts away. If it's fifty fifty, then the area will be thin but the lack of bent will allow the existing grass to thicken up a bit, and if it's KBG, then over time it will spread to fill in the voids.

These spots are mostly all bentgrass so why not just use Roundup in that case?

Interesting observation I made last night...when I walk across these areas after a decent rain the ground is soggy under them, whereas the rest of the lawn isn't. Is that a characteristic of bentgrass?

I'm thinking that in mid-September I will outline the areas with spray paint one morning (when most visible), kill them with roundup later that afternoon (when the grass is dry), rake up the dead grass in a week, and then re-seed with JG's Black Beauty.

If they are all bent then you can do that, it's cheaper and kill is total. Bentgrass doesn't make the ground soggy, it looks like the areas in your picture is in somewhat of a small valley, which is probably why it's wetter there, and, or there could be some soil differences. Mid Sept. is too late for NJ. You can seed anytime after Round-Up, but if you want to wait for it to all die then you want to apply it about two weeks before seeding. So mid August would be better, that would give you a seeding date around Sept.1. It all depends on what kind of grass seed you want to sow too, since KBG takes longer to germinate and mature, while TTTF or PR takes less time.

If you are going to spray Roundup, here is a tip you might find helpful. Spray your areas first thing in the morning. That is when the stomata of the leaves are more open, and the active ingredient (glyphosate) will penetrate into the plant more quickly and effectively. Plus, the wind is usually less active early in the morning.

Okay, so the modified plan is to spray Round Up mid-August (first thing in the morning) and seed on Sep 1.

Some followup questions:

1) What is KBG, TTTF, PR?

2) How do I best match the seed that I should use to the existing lawn? If I don't match it up right, then I'll just have the same type of problem with the new lawn, won't I? I don't really trust the advice of my local garden centers because their advice givers are mostly young kids.

3) Regular Round Up or Total Ground Clear?

4) How is that I can seed right after Round Up? Doesn't the active ingredient sit in the soil?

5) How do I prepare area the area for seeding after Round Up kills off the grass? Is raking the dead grass enough? Does raking dead grass bring the roots up easily? Or do I have to scalp a few inches of the ground to get the grass roots with a spade shovel?

2. It's tough because if you don't know what you have, or you know what you have but use the wrong cultivars you can get a mismatch. From the looks of your lawn I would say you probably have a mix of species, a typical northern mix which generally contains some KBG, PR and fine fescues or tall fescue. Unfortunately even those can look different if your lawn is an older one, i.e. has been the same lawn for a decade or more.

3. Anything that has glyphosate as its main ingredient will do. Every manufacturer has a different name for their non selective herbicide, but they all work.

4. Round Up only works if it's taken in by a plant foliarly. Round up in the soil is deactivated in a short time as well, so it wouldn't be an issue even if it worked like that.

5. Scalping the dead areas is enough. You don't have to disturbed the soil at all. It might be easiest to use a weed whacker to scalp those areas instead of a lawn mower. The old roots will provide organic matter as they decompose, so leave them right where they are. You can apply a light layer of good, weed seed free top soil if you want, but it's not necessary. I like to topdress my seeds, as I feel you get better seed to soil contact, and it helps keep the seeds moist longer.

I had the same thing, the bentgrass was spreading out is several circles, getting larger year over year. Nuked them with roundup, waited a couple of weeks and replanted and it was very successful. Did this is late August and was fortunate that we got some rain, as it was at the back end of the property and I did not water there.

Tiemco thanks for all your help. You answered every question I had. Mondo thanks for sharing your experience, makes me feel positive about killing off the large sections of bentgrass.

I'd still like to know why I have it and not my neighbors. The previous owners of my house used a landscaping company. Cross contamination from a previous mow earlier that day? And it's only on one side of my house. Could have been where the mower started that day?